The skin is an organ that covers the entire skin of the body and performs immune functions. Also, it is a tissue that protects the body from various harmful environments such as external microorganisms, UV rays and chemical substances and inhibits the evaporation of water from the body to prevent the dehydration of the body and control the body temperature. The skin should be strong against physical stimuli, should be elastic and should perform its functions when the human body maintains life. Thus, when the skin is wounded, such important functions become abnormal so that the human body is out of balance.
Wound treatment is a biological process for restoring tissue broken by any trauma or surgery and is an important process enabling the patient to be treated. Methods for treating wounds can be largely divided into a method of treating a wound by maintaining it in a dry state using, for example, a gauze dressing, and a method of maintaining a wound in a moist state.
The results of clinical studies, which have been conducted on moist dressings that maintain wounds in a moist environment, demonstrate the safety and effectiveness of a moist environment provided by a moist dressing in the treatment of acute wounds and chronic wounds that have been considered to be impossible to treat. In other words, in a moist environment, wound healing proceeds efficiently, because regenerated epithelial cells are easily developed along the wound surface and because substances, such as polymorphonuclear leukocytes, macrophages, proteases and cell growth factors, which are contained in exudate and involved in wound healing, can easily perform their functions in the moist environment.
Meanwhile, silver (Ag) has been known to have excellent antibacterial and bactericidal activities compared to other metals, and the antibacterial action and mechanism of silver has been scientifically verified through systematic studies conducted by many scientists together with the development of modem science. Silver has been used long ago as a perfect antibacterial material in the medical field, and the effect thereof was considered to be equal to artificial antibiotics prepared by synthesis, and silver causes no side effects.
At present, commercial antibacterial dressings comprising silver exist. The use of silver in cotton and bandages in hospitals is because the effects of silver against burns, infections, inflammation and other microbial infections were already scientifically proven. Colloidal silver as an aqueous solution is a natural antibiotic approved by the FDA and is currently used as an effective drug together with melatonin and DHEA in the USA. However, prior art technologies of absorbing silver into cloth using electrolyzed water and drying the cloth in order to use silver as medical supplies have shortcomings in that the content of silver is insignificant and silver is detached from the medical supplies during preparation, transport and use, and thus the effect of silver is rapidly lost.
U.S. Pat. Nos. 6,719,987 and 6,087,549 disclose electrocoating silver nanoparticles on a polyurethane mesh fiber having a monolayer structure, but have shortcomings in that silver is excessively contained, and thus is highly toxic against normal cells, and in that silver is detached from the product. In addition, there is also a shortcoming in that the product lacks the capability to absorb exudate, and thus cannot provide a moist environment. In addition, U.S. Pat. No. 6,897,349 discloses physically diffusing or dispersing silver nanoparticles, which have been precipitated by a chemical reaction, between fiber tissues, but the product disclosed therein does not exhibit sufficient antibacterial activity and sufficient therapeutic effects due to its low silver content. In addition, products obtained using such silver nanotechnologies have common problems in that the size and shape of nanoparticles are not uniform, it is not easy to control the particle size distribution, it is difficult to control the concentration and content of silver, and the production cost is high.
Meanwhile, chitosan is a kind of polysaccharide present in nature and is a compound obtained by deacetylating chitin contained in the shell of crabs and shrimps, the bone of cuttlefishes, and the cell wall of microorganisms such as fungi and bacteria. It has been used in various industrial fields from the middle of 1980s. The major application of such chitosan was limited to wastewater treatment applications, including flocculants, heavy metal adsorbents, and dye wastewater purifying agents, and agricultural applications, including soil improvers, insecticides, plant antiviral agents, and agricultural chemicals. However, as the advantages and various characteristics of chitosan have been found, the range of application of chitosan has been expanded to the food and beverage field, the health and hygiene field, the cosmetic field, the fiber-related field, and the medical field. Particularly, chitosan have received attention as a material usable as a medical material from 1990s, the use of chitosan in wound healing agents, artificial skins, medicinal materials, blood coagulants, artificial kidney membranes, biodegradable surgical sutures, and antimicrobial materials, has been reported.
More specifically, German Patent Nos. 1,906,155 and 1,906,159, which can be considered the first patents relating to wound dressings related to chitin and chitosan, disclose that chitin powder shows an excellent effect on wound repair, and U.S. Pat. Nos. 3,632,754 and 3,914,413 disclose that chitin promotes wound healing and is dissolved in lysozymes, indicating that it can be dissolved in a physiological environment. In addition, Japanese Patent Laid-Open Publication No. Sho 57-143508 discloses a gauze prepared from chitin fiber, and Japanese Patent Laid-Open Publication No. Hei 5-92925 describes the facts that the use of chitosan/cotton and chitin/cotton as a burn treating agent shows excellent effects of protecting wounds and alleviating pain, and it discloses a process of preparing chitin sponge by dispersing liquid chitin in water at a concentration of 1.5% (w/v), and pouring the dispersion onto a polystyrene film, followed by freeze drying.
Moreover, U.S. Pat. No. 4,651,725 discloses a method of preparing a wound dressing made of a non-woven fabric of chitin fiber; U.S. Pat. No. 4,699,135 discloses a method of preparing a wound dressing made of a non-woven fabric or fibrous sheet of a fibrous chitin body; Korean Patent Laid-Open Publication No. 2001-79260 discloses a method of preparing a dressing material using cultured chitosan short fiber; Korean Patent Laid-Open Publication No. 2001-67991 discloses a to method of preparing a functional fiber containing chitosan; and Korean Patent Laid-Open Publication No. 2000-14189 discloses a method of preparing a non-woven fabric for wound treatment using Chitin, chitosan and alginic acid.
Conventional gauze-type dressings as described above easily absorb a wound exudate, but have problems in that they have no ability to defend against external bacterial infections, maintain a wound in a dry state to delay wound treatment, and stick to the wound surface so that they are not easily replaced and cause damage to newly formed tissue and pain. In addition, there is an inconvenience in that the dressing should be replaced several times a day in the initial stage of wound healing, because a large amount of exudate occurs in the initial stage.
Wound-healing dressings prepared from chitin and chitosan that are natural polymers have advantages over conventional products prepared from synthetic polymers. Wound-healing dressing products comprising chitin/chitosan have high biocompatibility compared to conventional products, and thus exhibit an excellent effect of treating wounds themselves. In addition, these products have high abilities to adsorb harmful chemical substances and heavy metals, and thus can exhibit the effect of neutralizing a poison.
The present inventors have paid attention to the above-described problems occurring in the prior art and the effects of the natural polymer chitosan and conducted many studies on an antibacterial wound dressing which has sufficient antibacterial activity and an excellent ability to absorb exudate so as to provide a moist environment, and also has an excellent property of releasing an antibacterial substance in a sustained manner, and thus can maintain antibacterial activity in the wound area of the patient's skin for a long period of time. As a result, the present inventors have found that, when silver is mixed with chitosan, chitosan is ionically bonded to silver to form fine chitosan-silver nanoparticles which are uniformly coated on a wound dressing, which then has an excellent property of releasing the antibacterial material silver in a sustained manner, thereby completing the present invention.